The present invention relates to an optical switch for making light in an optical waveguide selectively emergent therefrom, and a display unit on which the optical switches are arrayed.
In home televisions, a cathode-ray tube having a mechanism of emitting light by exciting phosphors with electron beams is used as a display. In liquid crystal displays, a light transmittance is changed by varying a polarization characteristic of liquid crystal. In these liquid crystal displays, a color of white light is selected by using a filter. In plasma displays, phosphors are excited with ultraviolet rays generated by plasma.
By the way, television receivers have disadvantages that a depth of a cathode-ray tube is long, thereby making it impossible to realize a thin display, and that the weight of the cathode-ray tube is heavy. A further disadvantage of the television receivers is that since light emission is obtained by exciting phosphors, a half-width of an emission spectrum of each of three primary colors is large, to degrade a color purity and a color reproducing characteristic. Liquid crystal displays have a disadvantage that since a half-width of an emission spectrum determined by a color filter is also large, to degrade a color purity and a color reproducing characteristic. Plasma displays have disadvantages that since light emission is obtained by exciting phosphors like cathode-ray tubes, a half-width of each emission spectrum is large, to degrade a color purity and a color reproducing characteristic, and that it is not easy to adjust gradation of an image.
On the other hand, as display units utilizing photonics, there are known display units using optical waveguides. Such a display unit, however, has a problem that a contrast ratio of light emergent in response to turn-on/turn-off of an optical switching device, that is, an optical switch such as liquid crystal is low. Further, an optical switch having a structure in which light transmissive layers are stacked has another problem that a slight change in light emergence efficiency depending on a thickness and a refractive index of each layer of the stacked structure may exert a large effect on an uniformity of the entire light emergence efficiency, and therefore, it is expected to provide an optical switch capable of easily realizing the uniformity of a light emergence efficiency.
An optical switch composed of an optical waveguide including at least a cladding layer, and a light directivity coupler having an electrode film, an alignment control film, and ferroelectric liquid crystal filled between a pair of substrates is known, for example, from Japanese Patent Laid-open No. Hei 8-36196. The design of this optical switch aims that a coupling efficiency (light emergence efficiency) becomes 1, that is, a transfer rate of light becomes 100% by optimizing a refractive index of liquid crystal, and with respect to such design of the optical switch, the above document describes that the coupling efficiency can reach 98% by setting an effective refractive index of liquid crystal to 1.523.
An optical switch designed to pursue a high coupling efficiency as the optical switch described in the above document, however, has a problem. Namely, a refractive index of each component such as ferroelectric liquid crystal, an optical waveguide, an electrode film, or an alignment control film may be deviated from a design value due to variations which occur depending on a thickness and a material characteristic of each layer in production steps, and if the refractive index of a component is deviated from a design value, then such a deviation cannot be canceled only by adjusting a refractive index of ferroelectric liquid crystal, and the coupling efficiency is largely degraded as the deviation in the refractive index of the component from the design value becomes large, thereby failing to obtain the uniformity of a light emergence efficiency.
An object of the present invention is to provide an optical switch capable of significantly improving a contrast ratio, obtaining a clear, bright image, and easily realizing the uniformity of a light emergence efficiency, and to provide a display unit using the optical switches.
To achieve the above object, according to a first aspect of the present invention, there is provided an optical switch for making part of incident light, which contains a specific polarized light component and has been made incident on an optical waveguide, selectively emergent from the optical waveguide to a light emergence portion provided outside the optical waveguide, the optical switch including: a multi-layer structure composed of a plurality of light transmissive layer; wherein letting "sgr" be a refractive index control accuracy at the time of producing the multi-layer structure, a refractive index of at least one light transmissive layer in the multi-layer structure is different from a refractive index of a light transmissive layer other than the at least one light transmissive layer in the multi-layer structure by 3"sgr" or more.
According to a second aspect of the present invention, there is provided an optical switch for making part of incident light, which contains a specific polarized light component and has been made incident on an optical waveguide, selectively emergent from the optical waveguide to a light emergence portion provided outside the optical waveguide, the optical switch including: a light transmissive stacked structure including a function layer for selective emergence of the incident light; wherein letting xcex94n be a difference between a refractive index n0 of the optical waveguide and a refractive index n1 of an arbitrary layer forming part of the stacked structure, xe2x80x9cdxe2x80x9d be a thickness of the arbitrary layer, and xcex be a wavelength of the incident light, the values of xcex94n, xe2x80x9cdxe2x80x9d, and xcex satisfy a condition of 2.20xc3x9710xe2x88x923xe2x89xa6|xcex94nxc2x7dxc2x7xcexxe2x88x921|xe2x89xa63.03xc3x9710xe2x88x923.
According to the second aspect of the present invention, there is also provided a display unit including: a plurality of optical waveguides, disposed approximately in parallel to each other, for receiving light containing a specific polarized light component as incident light; one or two or more light emergence portions crossing the optical waveguides; and optical switches, disposed between the waveguides and the light emergence portions, for making part of the incident light selectively emergent from the optical waveguides to the light emergence portions provided outside the optical waveguides; wherein each of the optical switches has a light transmissive stacked structure including a function layer for selective emergence of the incident light; and letting xcex94n be a difference between a refractive index n0 of the optical waveguide and a refractive index n1 of an arbitrary layer forming part of the stacked structure, xe2x80x9cdxe2x80x9d be a thickness of the arbitrary layer, and xcex be a wavelength of the incident light, the values of xcex94n, xe2x80x9cdxe2x80x9d, and xcex satisfy a condition of 2.20xc3x9710xe2x88x923xe2x89xa6|xcex94nxc2x7dxc2x7xcexxe2x88x921|xe2x89xa63.03xc3x9710xe2x88x923.
With these configurations of the second aspect of the present invention, in which a value of xcex94nxc2x7dxc2x7xcexxe2x88x921 is specified, even if a refractive index of each layer of the light transmissive stacked structure of the optical switch is fluctuated, the light emergence efficiency is not varied so much. To be more specific, as a result of calculation, it is revealed that a small change region, in which the light emergence efficiency is not largely changed even if the refractive index n1 of an arbitrary layer is fluctuated and is somewhat deviated from a design value, is present in the vicinity of a refractive index portion at which the light emergence efficiency is maximized. By making effective use of such a small change region, it is possible to suppress a variation in light emergence efficiency even if the refractive index of an arbitrary layer is varied. The small change region in which the light emergence efficiency is not largely changed appears under a condition that a deviation in phase of light passing through an arbitrary layer (refractive index: n1, and thickness: xe2x80x9cdxe2x80x9d) is within a specific range. A value of xcex94nxc2x7dxc2x7xcexxe2x88x921 expresses the deviation in phase of transmission light, and the above condition for suppressing the light emergence efficiency by making use of the small change region is given by an expression of 2.20xc3x9710xe2x88x923xe2x89xa6|xcex94nxc2x7dxc2x7xcexxe2x88x921|xe2x89xa63.03xc3x9710xe2x88x923. The uniformity of the light emergence efficiency can be realized by setting the arbitrary layer under the above condition.
According to a third aspect of the present invention, there is provided an optical switch for making part of incident light, which contains a specific polarized light component and has been made incident on an optical waveguide, selectively emergent from the optical waveguide to a light emergence portion provided outside the optical waveguide, the optical switch including: a light transmissive stacked structure including a function layer for selective emergence of the incident light; wherein letting L xcexcm be a length of the function layer in the longitudinal direction of the optical waveguide, a thickness of the optical waveguide is in a range of 0.05xc2x7L xcexcm to 0.2xc2x7L xcexcm.
According to the third aspect of the present invention, there is also provided a display unit including: a plurality of optical waveguides, disposed approximately in parallel to each other, for receiving light containing a specific polarized light component as incident light; one or two or more light emergence portions crossing the optical waveguides; and optical switches, disposed between the waveguides and the light emergence portions, for making part of the incident light selectively emergent from the optical waveguides to the light emergence portions provided outside the optical waveguides; wherein each of the optical switches has a light transmissive stacked structure including a function layer for selective emergence of the incident light; and letting L xcexcm be a length of the function layer in the longitudinal direction of the optical waveguide, a thickness of the optical waveguide is in a range of 0.05xc2x7L xcexcm to 0.2xc2x7L xcexcm.
With these configurations of the third aspect of the present invention, in which a thickness of an optical waveguide is specified, a light intensity at one optical switch or at one pixel can be set to a high value. To be more specific, if the thickness of the optical waveguide is excessively thin as compared with a size of a function layer for selective emergence of the incident light in the optical switch, a mode number of a spectrum of light allowed to enter the optical waveguide is reduced, so that it is difficult to obtain a sufficient light intensity. On the other hand, if the thickness of the optical waveguide is excessively thick as compared with the size of the function layer, the probability that a light ray of one mode enters the function layer of one optical switch is reduced, so that it is impossible to obtain a sufficient light intensity even by performing selective emergence of light. Accordingly, to optimize the light intensity, it may be desirable to specify a range of the thickness of the optical waveguide. To be more specific, letting L xcexcm be a length of the function layer in the longitudinal direction of the optical waveguide, the thickness of the optical waveguide may be set in a range of 0.05xc2x7L xcexcm to 0.2xc2x7L xcexcm in order to optimize the light intensity.
According to a fourth aspect of the present invention, there is provided an optical switch for making part of incident light, which contains a specific polarized light component and has been made incident on an optical waveguide, selectively emergent from the optical waveguide to a light emergence portion provided outside the optical waveguide, the optical switch including: a light transmissive stacked structure including a function layer for selective emergence of the incident light; wherein letting xcex94n be a difference between a refractive index n0 of the optical waveguide and a refractive index n1 of an arbitrary layer forming part of the stacked structure, xe2x80x9cdxe2x80x9d be a thickness of the arbitrary layer, and xcex be a wavelength of the incident light, the values of xcex94n, xe2x80x9cdxe2x80x9d, and xcex satisfy a condition of |xcex94nxc2x7dxc2x7xcexxe2x88x921|xe2x89xa63.03xc3x9710xe2x88x923 and |xcex94nxc2x7dxc2x7xcexxe2x88x921|xe2x89xa00.
With this configuration of the fourth aspect of the present invention, since the range of a deviation in phase of transmission light, which is expressed by xcex94nxc2x7dxc2x7xcexxe2x88x921, is extended, the production of an optical switch becomes easier than the production of the optical switch under the above-described condition specified according to the second aspect of the present invention. In addition, since a value of xcex94n may become negative, the deviation in phase of transmission light is expressed by an absolute value of xcex94nxc2x7dxc2x7xcexxe2x88x921.